The preparation of overbased calcium or barium salts of carboxylic acids with alkyl phenols is disclosed in the following U.S. Pat. Nos. 2,616,904; 2,760,970; 2,767,164; 2,798,852; 2,802,816; 3,027,325; 3,031,284; 3,342,733; 3,533,975; 3,773,664; 3,779,992; 4,665,117; 5,830,935; and 5,859,267. The use of these overbased metal salts in halogen-containing polymers is also described in the aforementioned patents. Furthermore, these prior art patents also discuss the use of alkyl phenol as a promoter in the manufacture of the overbased metal salts.
According to the teachings of U.S. Pat. Nos. 4,665,117 and 5,859,267, for example, alkali or alkaline earth metal salts are prepared where alkyl phenol is used as a promoter of the reaction. However, alkyl phenol is also a major cause for the development of color in the final product and in stabilized PVC compositions. These patents also address the color stability issues of over-based alkyl phenates by applying propylene oxide, alkyl glycidyl esters, phosphites, and other such additives to restrict the formation of colored species which detract from the applications where a light-colored polymer product is desired. However, a number of disadvantages associated with the toxic nature of propylene oxide as a color inhibitor have been documented. Furthermore, due to recent legislation, primarily in Europe and Asia, with the accompanying impact on U.S. suppliers, there exists a need for a phenol-free overbased metal carboxylate. Also, environmental concerns with existing polymer stabilizers have stimulated interest in alternative stabilizers for the replacement of heavy metal stabilizers. As part of the voluntary initiative of Vinyl 2010, the European Vinyl Industry (EVI) is also committed to replacing heavy metal stabilizers and overcoming toxicity in all PVC applications by 2015. Thus, there has been considerable interest in making phenol and alkyl-phenol free PVC stabilizers, especially overbased metal stabilizers, and developing a new generation of environmentally acceptable PVC stabilizers that prevent degradation and change in color during processing, and also provide tangible benefits to the manufacture of useful articles.